Lab 6: Platyhelminthes, Gastrotricha

Transcription

1 Lab 6: Platyhelminthes, Gastrotricha Platyhelminthes 9 March 2016 Experiment: Planarian Regeneration (freshwater only!) As you have learned in class, these flatworms have incredible regeneration abilities. Working in pairs, make as many experiments as you want (you can add extra pages to the handout if you want to do more experiments), but be sure to replicate each experiment with at least two individuals. Because the animals secrete mucus continuously, you may need to clean your blade with Kimwipes frequently. Use plastic pipettes to move the animals/fragments between dishes. The animals will keep moving at room temperature, making cuts difficult. Keep the planarian dishes on ice until you have decided which experiments you will try. Follow these guidelines to make sure that you don t waste your work today: 1. Label every experiment. Include your name, the date, and an ID for the experiment (with a diagram of the cut you made to make follow up observations easier). 2. If you have cut your animals into more than one fragment, make sure each fragment is in a separate dish, labeled to indicate the origin of the fragment. 3. After your dissection and cutting, pour off the water and add fresh water to your dishes. 4. Keep every petri dish covered to prevent evaporation. 5. Place your experiments in the labeled area in the backbench for when you return. 6. Arrange with your group to change the water every day. 7. Make observations (drawings/notes) on the planarians tomorrow, on Friday and right after the fieldtrip on the 21 st. This handout will be due by 5pm on the 21 st. Here is a table of (a few) possible cuts: (but don t feel limited to it!) After the end of the experiments: Do the results match the predictions you made? Yes No Discuss your results in light of the predictions you made. What is one molecular mechanism related to regeneration in planarians? 1

2 EXPERIMENT 1 Explain prediction: Lab partner: Date Sketches of animals Notes Mar 9 cuts of your experiments Mar 10 Mar 11 Mar 21 2

3 EXPERIMENT 2 Explain prediction: Lab partner: Date Sketches of animals Notes Mar 9 cuts of your experiments Mar 10 Mar 11 Mar 21 3

4 Diversity of Platyhelminthes CHOOSE ONE PARASITIC FORM Neodermata (parasitic) For the following species, identify major organ systems. How do they differ from free- living Platyhelminthes? Also look up their names on the Internet to see which diseases they cause and what are the consequences and the prophylaxes. Trematoda (flukes) Most members of this group use two or more hosts during their life cycle. - Fasciola hepatica This flatworm is the liver fluke that commonly infects livestock and has a life cycle that requires snails as intermediate hosts, which are then eaten by livestock where the flukes mature. Draw this specimen from the slide. Identify and label internal structures and the zygotes visible in the uterus (see books and printed figure for assistance). - Schistosoma mansoni This is a significant parasite of humans what disease does it cause? They are atypical trematodes in that the adult stages have separate sexes instead of being hermaphroditic, and are found in the blood vessels of the definitive host, instead of the intestinal tract or other organs. 4

5 Cestoda (note the host origin and date collected!) These tapeworms lack a digestive tract or any vestiges of a mouth and therefore all nutrients must be taken through the tegument. Humans are subject to parasitism when eating undercooked meat such as pork (Taenia solium) and beef (T. saginata), or when eating food prepared in conditions of poor hygiene. Taenia saginata can grow up to 20 m (65 ft) in a person s intestines. - Taenia pisiformis (hosts: rodents, carnivores) cysticercus slide Taenia sp. (ethanol) Look at these preserved cestodes. Observe the reproductive anatomy and the morphology of the scolex. What is the name of the units along the body? What are they for? Which are the oldest? - Dipylidium canium slide Dipylidium sp. (in ethanol) The cucumber tapeworm infects pets through fleas, sometimes passing to humans as well. Observe the reproductive anatomy and morphology of the scolex. What is the name of the units along the body? What are they for? Which are the oldest? 5

6 CHOOSE ONE Polycladida (free- living) Thysanozoon brocchii (preserved in ethanol) Draw and label visible structures in this flatworm. Where is the mouth in free- living flatworms? Tricladida Planarians (live and on slide) Observe the external anatomy of the brown planarians and look for internal structures in the slide. Draw and label. Bdelloura candida These small flatworms occur on the legs of horseshoe crabs, adhering by a glandular caudal adhesive disk. Draw and label visible structures. Make a slide if there is not much you can see with the stereoscope. What do the names of these free- living groups refer to (Polycladida, Tricladida)? How is the shape of the referred structure related to the general body plan of these flatworms (flat acoelomates)? 6

7 Gastrotricha Gastrotrichs are widely distributed and abundant in freshwater and marine environments. They are mostly benthic and live on and between particles of sediment. These small invertebrates are detritivores, sucking dead or living organic material with the muscular pharynx. They move with cilia or by adhering their adhesive glands like a looper caterpillar. They are simultaneous hermaphrodites with direct development and have lifespans of only a few days. Lepidodermella sp. Put a drop from the gastrotrich jar in a slide. Can you recognize which moving organisms are gastrotrichs? Observe one moving and then find a slower specimen so you can draw it. Label as much as you can, using books and the printed scheme to guide your observations. What does the name Gastrotricha refers to? 7